1. Field of the Invention
The present invention generally relates to electrical sockets used to mount electrical components on a circuit board. More particularly, the present invention relates to interposer sockets and more particularly still to an interposer socket that includes a self-locking feature.
2. Background of the Invention
For many decades, circuit boards, such as those used in computers, have been manufactured by attaching electrical components to the board. In some cases, the components are soldered directly to the board. Although generally satisfactory, soldering a component directly to the board makes it difficult and costly to change that component should it be desired or necessary to replace one component with another. A microprocessor, for example, may have hundreds of connections that, should the processor fail, must be desoldered. A new processor, with its hundred of connections must then be attached to the board. Further, this process must occur without damaging the other components mounted on the circuit board. Even if the processor has not failed, it still might be desired to replace it, for example, when a new and improved version of the processor is made available.
For these and other reasons, “interposer” sockets have become available. Although defined in various ways, an interposer socket is a socket through which a chip (e.g., a microprocessor) is secured to a circuit board without the use of solder. One type of conventional interposer socket arrangement includes four threaded posts on to which various components are disposed such as the circuit board, a heat sink and the like. Springs are then inserted over the posts and held captive by screws connected to the threaded posts. This basic arrangement is illustrated in FIG. 1. An electronic component 10 is “sandwiched” between a heat sink 12 on one side and a base plate 14, circuit board 22 and socket 24 on the other side. Posts 20 extend up through the heat sink and are internally threaded on their upper end 26. Screws 16 compress springs 18 when threaded and tightened into threaded posts 20. The compression of the springs secures the component 10 to the socket 24 and circuit board 22.
The electronic component 10 typically has numerous electrical contacts (referred as “bumps”) under the component, which are not specifically shown in FIG. 1. It is generally known that each such contact or bump must have a suitable amount of compressive force (approximately 100 grams) in order to maintain its contact integrity over a 10 year product life. That is, for various reasons, over time substantially less than 100 grams of force per bump may eventually result in an insufficient electrical contact with regard to one or more of the bumps. Such reasons include, for example, “creep” in which a material being compressed naturally gravitates over time toward a certain shape and dimensional thickness. Thus, the amount of creep in the various components shown in FIG. 1 must be considered when determining the initial compressive force from the springs.
Although generally effective, this conventional Interposer socket arrangement does have at least one shortcoming. As the size of the electrical components being retained by such socket increases, the number of bumps increases as well. It is not uncommon today to have a microprocessor package designed for Interposer mounting that has 1443 bumps. Because each bump still must have the predetermined amount of compressive force (e.g., 100 grams per bump), the total amount of compressive force on the chip has become quite large requiring hundreds of pounds of total force. An increase in force can be achieved through the use of stiffer springs 18 (having a larger spring constant). Turning the screws 16 under such large total force occasionally can cause conditions known as galling and/or “cold welding.” This condition has to do with the friction between the threads of the screws 16 and the corresponding threads of the posts 20. As the total force increases with the use of stiffer springs, the friction increases and, in a relatively small percentage of cases, actually can cause the screw 16 to become welded to the post 20 preventing the screw from being turned further, preventing sufficient force to be applied to the component and perhaps causing the screw to break. Also, metallic particles can be created when the screws are tightened which can short some of the contacts and cause damage to the chip.
Obviously, these sorts of problems are undesirable. These problems will no doubt become even more severe as chip size grows. Anything that can be done to avoid such problems is highly desirable.